The present invention relates generally to an inspection system and an inspection method. More particularly, the present invention relates to an inspection system for and a method of inspecting a pattern on a reticle or photomask for defects and errors.
Semiconductor fabrication techniques often utilize a mask or reticle. Radiation is provided through or reflected off the mask or reticle to form an image on a semiconductor wafer. The wafer is positioned to receive the radiation transmitted through or reflected off the mask or reticle. The image on the wafer corresponds to the pattern on the mask or reticle. The radiation can be light, such as ultraviolet light, vacuum ultraviolet (VUV) light, extreme ultraviolet light (EUV) and deep ultraviolet light. The radiation can also be x-ray radiation, e-beam radiation, etc.
One advanced form of lithography is extreme ultraviolet (EUV) light lithography. A conventional EUV system (e.g., an optical reduction camera or stepper) utilizes an EUV radiation source, a first EUV lens assembly (e.g., a condenser lens), an EUV reticle, and a second EUV lens assembly (e.g., an objective lens). EUV radiation can be created at the EUV radiation source and projected onto the EUV reticle. The EUV reticle is typically a resonant-reflective medium including a pattern of absorbing material.
The EUV reticle reflects a substantial portion of the EUV radiation which carries an integrated circuit (IC) pattern formed on the reticle to the second EUV lens assembly. The first and second lens assemblies can be an all resonant-reflective imaging system including an aspheric optical system at 4:1 demagnification (e.g., a series of high precision mirrors). EUV radiation reflected off the EUV reticle is provided from the second EUV lens assembly to a photoresist coated wafer.
EUV lithography utilizes radiation in a wavelength ranging from 5 to 70 nanometers (nm) (e.g., 11-14 nanometers). A conventional EUV reticle can be a multilayer medium including an absorber pattern across its surface. The multilayer medium can utilize molybdenum/silicon (Moxe2x80x94Si) layers or molybdenum/beryllium layers (Moxe2x80x94Be). The absorber pattern can be one or more layers of material selectively arranged on a top surface of the multilayer medium. The actinic wavelength for an EUV system can be 13.4 nm.
Tools, such as, masks or reticles, for lithographic IC fabrication processes must be inspected to ensure that the proper pattern is present on the reticle and to ensure that defects are not present on the reticle. Defects can be introduced during the fabrication of the mask or reticle, during handling of the mask or reticle, and/or during use of the reticle in the EUV lithographic system. Inspections can verify that the mask or reticle has the proper physical characteristics, critical dimensions, and registration.
Inspections ensure that the photoresist material can be selectively formed within specified tolerances. For example, mistakes or unacceptable process variations associated with the mask or reticle should be corrected before any physical changes are produced on the wafer itself, such as, by doping, etching, etc.
Various techniques can be utilized to inspect masks and reticles. For example, optical microscopes, scanning electron microscopes (SEMs) and laser-based systems have been utilized for inspection tasks and line width measurement tasks. Holographic principles have even been used to detect defects on masks and reticles.
The amount of automation in these inspection tasks has varied. For example, human vision may be required in some inspection procedures to determine and classify defects. Other inspection tasks have been automated so that the human operator is completely removed from the defect inspection tasks. Automated mask or reticle inspection systems include the KLARIS system manufactured by KLA, the Chipcheck system manufactured by Cambridge Instruments, and the 8100 XP-R CD SEM manufactured by KLA-Tencor Corp. Defect detection and pattern verification in these automated systems can be accomplished either by mask-to-mask or mask-to-standard comparisons.
One type of conventional automated defect detection system provides radiation or light from a light source to a surface of the mask or reticle being inspected. Light from the light source is directed through an optical system to the mask or reticle. The optical system focuses the light and can include mirrors, lenses, and prisms. The light strikes the surface of the reticle and is reflected. Alternatively, the light can pass through the mask.
The light reflected from the reticle or the light through the mask is sensed by photoelectric detectors. The light can be provided through an optical system including mirrors, lenses, and prisms. Generally, the light is analyzed to determine whether the appropriate image is on the reticle or mask and whether or not defects are present. Defects can include scratches, misalignment, line errors, contamination, dust, etc.
Conventional inspection systems utilizing conventional inspection pulse durations and wavelengths of light cannot adequately inspect EUV reticles or masks. EUV masks and reticles have a significantly different construction than reticles used in less advanced lithography. The contrast between the absorber pattern and the multilayer of the EUV reticle is poor at conventional inspection wavelengths and pulse durations. The contrast observed with conventional inspections systems has been fifty percent (50%) or less. Accordingly, ascertaining the correctness of the image on the EUV reticle as well as determining whether any defects are present on the EUV reticle is difficult with conventional inspection systems.
Thus, there is a need for a highly accurate inspection system that can be utilized to detect defects and patterns on a mask or reticle. Further, there is a need for a semiconductor fabrication inspection tool for detecting defects and patterns on an EUV reticle. Even further still, there is need for a system for or a method of detecting patterns on an EUV reticle which obtains enhanced contrast and greater inspection functionality capability. Even further still, there is a need for an inspection tool and inspection method that is capable of reliably detecting patterns on an EUV reticle and capable of greater inspection capability. Yet further still there is a need for a modification to a conventional inspection system that allows it to effectively inspect EUV reticles.
An exemplary embodiment relates to an inspection system. The inspection system is used with a reticle including a multilayer and an absorbing pattern. The inspection system includes a light source and a detector. The light source provides an ultra-short pulse duration of the light. The detector is positioned to receive the light after the light is reflected off the reticle.
Another exemplary embodiment relates to a method of inspecting a reticle. The reticle is associated with the manufacture of an integrated circuit. The method includes providing radiation at a first pulse duration to the reticle and receiving the radiation at the first pulse duration reflected from the reticle. The method also includes providing radiation at a second pulse duration to the reticle and receiving the radiation at the second pulse duration reflected from the reticle.
Still another exemplary embodiment relates to an inspection system for an EUV reticle for use in an integrated circuit fabrication system. The inspection system includes means for providing radiation at a first pulse duration to the reticle and means for detecting the radiation at the first pulse duration reflected off the reticle. The first pulse duration is an ultra-short pulse duration.
Yet another embodiment relates to an inspection system for an EUV reticle for use in an integrated circuit fabrication system. The inspection system includes means for providing radiation at a first pulse duration to the reticle and means for detecting the radiation at the first pulse duration reflected off the reticle. The inspection system further includes a means for providing radiation at a second pulse duration to the reticle, means for receiving the radiation at the second pulse duration reflected off the reticle, and means for comparing the reflected radiation at the first pulse duration to the reflected radiation at the second pulse duration.